Project Summary/Abstract Fuchs Endothelial Cornel Dystrophy (FECD), a common age-related dystrophy, which is more prevalent in women, is of unknown etiology. In FECD, corneal endothelial (CE) cell loss is accompanied by abnormal extracellular matrix (ECM) deposition in the form of guttae. Our laboratory was the first to link oxidative DNA damage and mitochondrial dysfunction in FECD pathogenesis. Specifically, we showed that DNA damage, induced by ultraviolet-A (UVA) light, causes FECD in mice. Moreover, the UVA induced CE cell cycle arrest in G2/M phase and cellular senescence. We identified the novel involvement of CYP1B1, the key estrogen- metabolizing enzyme, in sex-dependent differences in CE susceptibility to UVA; and detected greater mitochondrial DNA (mtDNA) damage in female mice. However, the mechanism of the observed greater susceptibility of female mice to UVA-induced DNA damage is unknown. Building upon our previous findings, we propose to investigate if UV light?induced oxidant-antioxidant imbalance leads to senescence and ECM deposition by causing G2/M cell cycle arrest; and if this imbalance causes translocation of CYP1B1 into mitochondria triggering greater estrogen-induced mtDNA damage in females. Gene array analysis revealed downregulation of DNA repair genes in FECD; therefore, we will determine whether this leads to decreased DNA damage repair during G2/M cell cycle arrest, triggering the cells to undergo either senescence or apoptosis. Our study is significant, as the investigation sex-dependent mechanisms involved in oxidative stress-induced cellular damage will provide new treatment targets for FECD. In order to achieve these aims, we will use our newly developed non-genetic mouse model of FECD based on physiologic outcome of CE susceptibility to UVA along with immortalized human CE cell lines, human aqueous fluid, and ex vivo specimens of genotyped FECD donors. Our Specific Aims are: Aim 1: Investigate the role of UVA irradiation in G2/M cell cycle arrest and induction of cellular senescence and ECM deposition in FECD. This aim is based on the hypothesis that DNA damage leads to G2/M phase arrest and induces cellular senescence, which in turn leads to aberrant ECM deposition in the form of guttae in FECD. Aim 2: Determine whether UVA irradiation activates CYP1B1 and induces estrogen metabolism causing preferentially greater DNA damage in females. This aim is based on the hypothesis that higher incidence and severity of FECD in women occurs due to UVA- induced translocation of CYP1B1 into mitochondria, which triggers formation of reactive estrogen metabolites, causing mtDNA damage. Aim 3: Determine the role of DNA damage response and DNA repair during UVA- induced cell cycle arrest in FECD. This aim is based on the hypothesis that DNA repair deficiency during G2/M cell cycle arrest determines whether cells undergo senescence or apoptotic cell death in FECD.